Optical objective



00. W 1 ms 333mm 0&1

April 16, 1946. A. WARMISHAM 2,393,680

OPTICAL OBJECTIVE Filed Sept. 21, 1944 s Sheets-Sheet s R2 R3 R4 R5 R6R7 R8 R9 RIO Pl/ "Ma; w l M Inventor A Home y NHL- Patented Apr. 16,1946 Search Roan OPTICAL OBJECTIVE Arthur Warmisham, Leicester, England,assignor to Taylor, Taylor & Hobson Limited, Leicester, England, acompany of Great Britain Application September 21, 1944, Serial No.555,167 In Great Britain July 6, 1943 17 Claims. (CI. 88-57) Thisinvention relates to optical objectives for photographic or projectionor like purposes, of the kind corrected for spherical and chromaticaberrations, coma, astigmatism, field curvature and distortion andcomprising two compound dispersive meniscus components having theirconcave air-exposed surfaces facing one another disposed between a frontcollective component and a pair of rear collective components. It is tobe understood the term front as herein used refers to the side of theobjective nearer to the longer conjugate and the term rear to the sidenearer the shorter conjugate.

It is known in such an objective, in order to improve the correctionsfor spherical aberration and field curvature, to employglasses havingmean refractive index greater than 1.63 for the front element of thefront compound dispersive component, for the rear element of the rearcompound dispersive component and for the front member of the pair ofcollective rear components, the three collective components allconsisting of simple elements. In such known objective the two rearcollective components both have their shallower surfaces facing thefront and the optical power of the rear component lies between 40% and70% of the equivalent power of the whole objective.

The present invention has for its object still further to improve thecorrection of the abberations in an objective of the above mentionedkind.

In the objective according to the invention the mean refractive index ofthe material used for the rear element of the rear dispersive componentlies between 1.70 and 1.80, whilst the collective fourth component issimple and is made of a material having mean refractive index less than1.70, at least one of the two collective rear components having itsshallower surface facing the front.

The power (that is the reciprocal of the focal length) of the collectiverear component preferably lies between 30% and 70% of the power of thewhole objective. Conveniently the sum of the numerical values of theradii of curvature of the concave air-exposed surfaces of the twocompound dispersive components is greater than .5 and less than .7 timesthe equivalent focal length of the whole objective. The three collectivecomponents are preferably all in the form of simple elements.

Usually, both rear collective components will have their shallowersurfaces facing the front, and in such case the radii of curvature ofthe rear surfaces of these components lie between 1.5 and 4.0 times theequivalent focal length of the whole objective. This, however, is notessential to the invention, and one of these components, for example therear component, may have its shallower surface facing the rear. In suchcase the radii of curvature of the rear surfaces of the two componentspreferably lie between 1.3 and 6.0 times the equivalent focal length ofthe whole objective.

The rear element of the rear dispersive component may be made of opticalglass having the appropriate refractive index or alternatively it issometimes convenient to use crystalline magnesium oxide in the formknown as p-magnesiumoxide for this element. Such crystal may also beused for the collective rear component.

Figures 1-5 of the accompanying drawings respectively illustrate fivepractical examples of objective according to the invention, andnumerical data for these examples are given respectively in thefollowing tables, in which R1 R2 represent the radii of curvature of thevarious surfaces counting from the front (the positive sign indicatingthat the surface is convex to the front and the negative sign that it isconcave thereto) D1 D2 represent the axial thicknesses of the individualelements, and S1 S2 represent the axial air separations between thecomponents. The tables also give the mean refractive indices 11,, forthe D-line and the Abbe V numbers of the materials used for theelements.

Example I Equivalent focal length 1.000. Relative aperture F/l.5

Thickness Refractive Abbe V Radms gg gg index on number D1 1086 1. 613559. 3 RrHi. 166

S1 0020 Rg+ 3972 D3 1693 1. 6431 48. 3 Rrl-l. 471

D. 0313 1. 67605 32. 3 RH 2736 Sr 3106 Rs- 356B D4 0414 1. 621 36. 2R1+L 263 DI 1409 1. 7445 45. 8 Rr- 5351 Ss 0020 R|+4. 210

DI 0575 1. 613 59. 3 R 1. 683

S4 0020 Ru-Hi. 886 D1 0405 I. 6135 59. 3 R1) 2. 321 I Ezample Il'Equivalent focal length'lmo. Relative aperture F/1.5

Thickness Refractive AbbV Radius 55 35 index my number D: .1691 1.643148.3 Rel-7. 991

S3 .2003 Ra- 3639 Di .1504 1.7385 53.5 R| 5434 SA .0020 Ru+3. 364

Example III Equivalent focal length 1.000. Relative aperture F/1.5

Thickness R elractive Abbe V Radms ga ag index 12;; number Dr 1085 1.6135 53. 5 Ri-Hi. 157

S1 .0020 EH- .3966

D: .0313 1.67605 32.3 RH- .2735

D5 1504 1.7385 53.5 Rs- 5433 S: .0020 Re+4. 204

D0 .0575 1.613 53.5 Ray-1.841

S4 .00% Rn+3. 927

D: .0494 1.7385 53. 5 Rfl3. 157

Example IV Equivalent focal length 1.000. Relative aperture F/1.5

Thickness Refractive Abbe V Radius or air 7 separation index up numberD1 .1087 1.6135 53.5 Rr+6.l71

S1 .0020 I Rz+ .3975

D8 .0314 1.67605 323 RH .2741

S2 .2008 Ro- .3646

D4 .0415 1.608 3812 R1+l.264

D6 .1507 1. 7385 53.5 RI-- .5445

S: .0020 eri-2.984

D0 .0536 1.525 59.0, Rio-1.728

D1 .0496 1.7385 53.5 RIP-3.147

Example V The back focal lengths in these five examples are respectively.5731, .5692, .5717, .5714 and .5705 times the equivalent focal lengthof the objective. The ratio of the power of the rear component to thatof the whole objective is 42.3% in Example I, 42.3% in Example II, 42.2%in Example III, 42.2% in Example IV and 38.5% in Example V. Thenumerical sum of R5 and Re lies between .63 and .64 in all fiveexamples. In the first four examples the two rear collective componentshave their shallower surfaces facing the front, whilst in Example V therear component has its shallower surface facing the rear.

In Example I the rear element of the rear dispersive component is madeof optical glass, whilst in the other four examples magnesium oxidecrystal is used for this element. This crystal is also used for the rearcomponent in Examples III, IV and V, this component being made of densebarium crown glass in Examples I and II. Examples IV and V (which aresubstantially the same except for the curvatures of the last threesurfaces) differ from the first three examples primarily in the use of alow index glass forthe collective fourth component.

' What I claim as my invention and desire to secure by Letters Patentis:

V 1. An optical objective, corrected for spherical and chromaticaberrations, coma, astigmatism, field curvature and distortion andcomprising a collective front component, two co ound dispersive meniscuscomponenm gsgd behind such component, the concave air-exposed surfacesof such dispersive components facing one another and having radii ofcurvature whose numerical sum lies between .5 and .7 times theequivalent focal length of the whole objective, 2. simple collectivefourth component made of a material having mean refractive index lessthan 1.70, and a collective fifth component, whose optical powerliesbetween 30% and 70% of the power of the whole objective, at least one ofthe rear pair of collective components having its shallower surfacefacing the front, the mean refractive index of the material used for therear element of the rear compound dispersive component lying between1.70 and 1.80.

, 2. An optical objective as claimed in claim 1, in which the collectivefourth component has its shallower surface facing the front, and thecolasoae'eo lective fifth component is in the form of a simple element.

3. An optical objective as claimed in claim 1. in which the collectivefourth and fifth components each have their shallower surfaces facingthe front.

4. An optical objective, corrected for spherical and chromaticaberrations, coma, astigmatism, field curvature and distortion andcomprising a collective front component, tw compound dispersive meniscuscomponents dis sed behind such component and having their concaveairexposed surfaces facing one another, a simple collective fourthcomponent made of a material having mean refractive index less than1.70, and a simple collective fifth component whose optical power liesbetween 30% and 70% of the power of the whole objective, the rearsurface of each of the rear pair of collective components being morestrongly curved than the front surface thereof and having radius ofcurvature between 1.5 and 4.0 times the equivalent focal length of thewhole objective, the mean refractive index of the material used for therear element of the rear compound dispersive component lying between1.70 and 1.80.

5. An optical objective, corrected for spherical and chromaticaberrations, coma, astigmatism, field curvature and distortion andcomprising a collective front component, two compound dispersivemeniscus components disposed behind such component, the concaveair-exposed surfaces of such dispersive components facing one anotherand having radii of curvature whose numerical sum lies between .5 and .7times the equivalent focal length of the whole objective, a simplecollective fourth component made of a material having mean refractiveindex less than 1.70. and a collective fifth component, the rear surfaceof each of the rear pair of collective components being more stronglycurved than the front surface thereof and having radius of curvaturebetween 1.5 and 4.0 times the equivalent focal length of thewholeobjective, the mean refractive index of the material used for the rearelement of the rear compound dispersive component lying between 1.70 and1.80.

6. An optical objective as claimed in claim 1, in which the collectivefourth component has its shallower surface facing the front and thecollective fifth component has its shallower surface facing the rear.

7. An optical objective, corrected for spherical and chromaticaberrations, coma, astigmatism, field curvature and distortion andcomprising a collective front component, two,eompound dispersivemeniscus components disposed behind such component .and having theirconcave airexposed surfaces facing one another, a simple collectivefourth component having its shallower surface facing the front and madeof a material having mean refractive index less than 1.70, and acollective fifth component having its shallower surface facing the rearand having optical power lying between 30% and 70% of the power of thewhole objective, the radii of curvature of the rear surfaces of the tworear collective components lying between 1.3 and 6.0 times theequivalent focal length of the whole objective, the mean refractiveindex of the material used for the rear element of the rear compounddispersive component lying between 1.70 and 1.80.

8. An optical objective, corrected for spherical and chromaticaberrations. coma, astigmatism, field curvature and distortion andcomprising a 363F011 WM) collective frontl'component, two compounddispersive meniscus components disposed behind such component, theconcave air-exposed surfaces of such dispersive components facing oneanother and having radii of curvature whose numerical sum lies between.5 and .7 times the equivalent focal length of the whole objective, asimple collective fourth component made of a material having meanrefractive index less than 1.70 and having its shallower surface facingthe front, and a simple collective fifth component having its shallowersurface facing the rear, the radii of curvature of the rear surfaces ofthe two rear collective components each lying between 1.3 and 6.0 timesthe equivalent focal length of the whole objective, the mean refractiveindex of the material used for the rear element of the rear compounddispersive component lying between 1.70 and 1.80.

9. An optical objective as claimed in claim 1, in which the collectiverear component consists of a simple element and is made of materialhaving mean refractive index between 1.70 and 1.80.

10. An optical objective as claimed in claim 1, in which the rearelement of the rear compound dispersive component is made of crystallinemagnesium oxide in the form known as fl-magnesium oxide.

11. An optical objective as claimed in claim 5, in which the rearelement of the rear compound dispersive component is made of crystallinemagnesium oxide in the form known as fi-magnesium oxide.

12. An optical objective as claimed in claim 8,

. in which the rear element of the rear compound dispersive component ismade of crystalline magnesium oxide in the form known as Si-magnesiumoxide.

13. An optical objective as claimed in claim 4. in which the rearelement of the rear compound dispersive component and the simplecollective rear component are both made of crystalline magnesium oxidein the form known as fl-magnesium oxide.

14. An optical objective as claimed in claim 7, in which the rearelement of the rear compound dispersive component and the simplecollective rear component are both made of crystalline magnesium oxidein the form known as fl-magnesium oxide.

15. An optical objective having numerical data substantially inaccordance with the following table:

Equivalent focal length 1.000. Relative aperture F/l.5

Thickness Refractive Abb V Radms 35 35 index 12 number D1 1086 1. 613550. 3 RH-B. 166

Si 0020 RH 3972 D: 0313 1. 67605 32. 3 Rs-i- 2736 S2 2006 Ro 3568 D40414 1. 621. 30. 2 R1+l. 263

D5 1409 1. 7445 45. 8 Ra- 5351 Se 0020 Ro+4. 210

Do 0576 1. 613 59. 3 Rio-1. 683

S4 0020 Bil-1'3. 886

D7 0495 1. 6135 59. 3 Rn-Z 321 wherein the terms R, D, and represent theradii of curvatureof the various surfaces counting from the front (thepositive sign indicating that the surface is convex to the front and thenegative sign that it is concave thereto), DIDZ represent the axialthicknesses of the individual elements, and 81S: represent the axial airseparations between the components; the tables also give the meansrefractive indices for the D-line and the Abbe V numbers of thematerials used for the elements.

16. An optical objective having numerical data substantially inaccordance with the following table:

Equivalent focal length 1.000. Relative aperture F/1.5

Thickness Refractive Abbe V Radius or air Separation index 1m number DI.1085 1.6135 53.5 Rz-Hi. 157

D: .1690 1.6431 48.3 Ri+7.090

S: .2003 Rs- .3638

D4 .0414 1.608 38.2 R1+1.26l3

DJ .1504 1.7385 53.5 Ra- .5433

St .0020 R|+4.204

De .0575 1.613 53.5 Rio-1.841

S4 .0020 Ru+3.927

D1 .0494 1.7385 53.5 R g-3. 157

wherein the terms R, D, and 8 represent the radii of curvature of thevarious surfaces counting from the front (the positive sign indicatingthat the surface is convex to the front and the negative sign that it isconcave thereto). D1D2 represent the axial thicknesses of the 1'7. Anoptical objective having numerical data substantially in accordance withthe following table:

Equivalent focal length 1.000. Relative aperture F/1.5

Thickness v Refractive AbbV 'Radms gg gfi index no number D1 .10871.6135 53.5 R1+6.l7l

St .0020 R +.3975

.0314 1.67605 32.3 Rs-l- .2741

D4 .0415 1.608 38.2 R1+L264 D5 .1607 1.7385 53.5 RI .5445

St .0020 [fa-F2934 D0 .0536 1. 525 59.0 Rio-1.555

s. .0020 Ru+3.37l

D1 .0400 I 1.7385 53.5 Bis-4.445

wherein the terms R, D, and 8 represent the radii of curvature of thevarious surfaces counting from the front (the positive sign indicatingthat the surface is convex to the front and the the tables also give themeans refractive indices n for the D-line and the Abb V numbers of thematerials used for the elements.

ARTHUR. WARMISHAM.

